Because zombie spamware regularly ignores MX priorities, we set up 4 MX records with 4 different priorities and made sure that our DNS was round-robined, meaning that the records would be returned in random order, but that doesn't matter to a complaint SMTP server which should choose the proper priority. Spamware seems to just simply choose the first MX record returned, so when round-robined, that means that zombie spamware is evenly divided over our 4 records. This is effective enough that we then use Declude to filter for hits on all but the primary MX record, and we add points for such hits. It is very effective since hits to our MX3 and MX4 are 99.9% spam. Hits on our MX2 are scored lower since their is more legitimate traffic that may hit it and it is on a separate box on a separate network. MX3 and MX4 are on the same box as MX1, so technically, those should almost never be hit by anything remotely legitimate.
Matt
R. Scott Perry wrote:
The only time that any legitimate traffic should flow through our "secondary
MX" is when the primary is down completely.
"never, ever" ??? not very humble, you "IMHO"
In practice, simply not true, so don't bet any money on it.
You are correct -- it the *remote* mailserver has a temporary problem with their Internet connection, the connection to the primary may fail, and the mailserver will contact the backup. So legitimate traffic definitely can go to the backup.
-Scott
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